In a commercial power system supplied by a power company, maintenance and management of power supply quality are mainly performed by the power company.
On the other hand, a self-sustaining power supply system which is not connected to the commercial power system needs to perform maintenance and management of the power supply quality by oneself. Examples of such a self-sustaining power supply system include a microgrid in which plural types of power supplies such as power generating installations such as a fuel cell power generating installation, a photovoltaic power generating installation, and a diesel power generating installation and power storage installations such as a secondary battery and an electric double layer capacitor are combined and networked in a certain area, and the like.
In the power generating installations such as the fuel cell power generating installation and the photovoltaic power generating installation or the power storage installation, a power conversion device is provided for each power supply, and power output from each power supply is controlled. There are two types of power conversion devices such as a current control type and a voltage control type according to a control method thereof
The current control type power conversion device is controlled to output a predetermined current regardless of a voltage or a frequency of a system connected thereto. The current control type power conversion device is mainly used as a power conversion device for system linkage. The voltage and frequency are premised to be maintained by other power generating installations (commercial system, motor generator, and the like), and the current control type power conversion devices cannot perform a self-sustaining operation alone or in combination.
On the other hand, the voltage control type power conversion device is controlled to output power with a constant voltage and frequency regardless of an output current. The voltage control type power conversion device is mainly used as a power conversion device for a self-sustaining operation alone. A linkage operation with the system and a parallel operation between the voltage control type power conversion devices cannot be used because the output becomes unstable.
For this reason, conventionally, in a case of switching from a state where the microgrid or the like operates in conjunction with the commercial power system to the self-sustaining operation, or from the self-sustaining operation to the commercial power system linked operation, the control method of the power conversion device needs to be switched.
In addition, in the self-sustaining power supply system, it is necessary to make the generated power and power consumption of a load coincide with each other all the times. Furthermore, when the power supply system is constituted by a plurality of power generating installations having different characteristics, it is necessary to appropriately adjust load sharing according to the characteristics of each power generating installation.
In order to solve such problems, PTL 1 discloses performing virtual generator model control which controls a power amount received from a power storage installation under the assumption that a virtual generator is connected to a power system, as a configuration which performs switching between a linkage operation with a power system and a self-sustaining operation without instantaneous interruption, performs autonomous load sharing among a plurality of power storage installations, or realizes system frequency stabilization in the short time.